Wool is a natural fibre obtained from sheep and consists mostly of protein components and minor lipid components.
Keratin proteins constitute 80% of the total fibre and are characterized by a significant content in cystine. The physical and chemical properties of wool are determined by the existence of this amino acid and by the nature and molecular weight of the lateral chains constituted by said proteins.
Despite being found in minority proportions, the lipid components of wool appear to fulfil an essential role in many of the physical-chemical properties of wool fibres. According to their position on the fibre, they can be classified into external lipids and internal lipids.
External lipids are found on the surface of wool fibres and are secreted by the animals' skin. These external lipids consist of saponifiable fats, non-saponifiable materials and traces of free inorganic acids in addition to other impurities. Lanolin is the wax obtained from wool once it has been purified, which is used for waterproofing and in skin treatment.
Various methods for extracting lanolin are described in the literature. Among these, one would cite those that use fluids in supercritical conditions, such as for example those described in Spanish patent applications ES-A-2186485 and ES-A-2161611, in patent application PCT WO-A-02/100990-A1, and in the articles by Alzaga et al., Anal. Chim. Acta, 1999, 381, 39-48, Eychenne et al., J. Supercrit. Fluids, 2001, 21, 23-31, Domínguez et al., Anal. Chim. Acta, 2003, 477, 233-242, Domínguez et al., J. Am. Oil. Chem. Soc., 2003, 80 (7), 717-724, Domínguez et al., Proceedings of the 10th International Wool Textile Research Conference, 2000, Aachen, and Domínguez et al., Proceedings of the 11th International Wool Research Conference, 2005, Leeds.
At the same time, internal lipids are found in the internal structures of the wool fibres, in what is referred to as the cellular membrane complex, in proportions that vary from 1.2% to 1.5% in relation to the total weight of the fibre.
Exhaustive analyses have been carried out and have identified free fatty acids, cholesterol, ceramides, and cholesterol sulphate as the main components of internal lipids.
One of the most valued components of internal wool lipids are ceramides, because, as described in Spanish patent application ES-A-2157807, they form a substantial part of the lipid barrier of human skin, which is responsible for protecting the same from environmental aggressions and maintaining the balanced hydration it needs for its good conservation.
In the state of the art, different methods have been used for extracting internal wool lipids. In general, the art of supercritical extraction using carbon dioxide provides extracts with a somewhat higher content in ceramides than that obtained with the conventional extraction art using mixtures of solvents; however, the performance of the extraction turns out to be lower.
Patent application ES-A-2157807, already mentioned above, describes a procedure for extracting internal wool lipids using carbon dioxide in supercritical conditions. This procedure uses wool that is substantially free of lanolin as the source material.
The extraction procedure described is carried out at a pressure of 340 atmospheres (344 bars), at a temperature of 100° C. and with 10% expressed in volume/volume of methanol as a co-solvent.
The performances of the extraction depend on the type of wool used. In the case of Spanish Merino wool, 0.290% of internal lipids are obtained over the initial weight of the extracted wool fibre, and in the case of New Zealand Merino wool, 0.355% is obtained. A quantitative analysis of the internal lipids made it possible to determine that 0.13% and 0.11% of ceramides had been extracted respectively over the total weight of extracted wool.
The article by Coderch et al., J. Am. Oil. Chem. Soc. 2002, 79 (12), 1215-1220 describes various procedures for the extraction of internal lipids from wool that is substantially free of lanolin in supercritical conditions using carbon dioxide.
In this article, different tests were carried out in varying conditions with two types of wool: Romney from New Zealand (R-NZ) and Merino from Spain (M-ES). The results of total extracted lipids, expressed as a percentage over the weight of extracted wool fibre, are summarized in the table below:
% of total lipidsPressureT% (v/v) ofover weightTestWool(bars)(° C.)Co-solventco-solventof the wool1R-NZ36060Methanol100.1432R-NZ360100Methanol100.2263R-NZ360160Methanol100.1884R-NZ360100Methanol200.1255M-ES36060Methanol100.1476M-ES360100Methanol100.2027M-ES10060Ethanol200.8818M-ES36060Ethanol200.564
One can see that the highest extraction performances were obtained in tests nos. 7 and 8 using a relatively high percentage of ethanol (20%) as the co-solvent.
According to the data appearing in this publication, in test no. 7 the extract contained 33% of ceramides, which represented an extraction of 0.29% of ceramides over the total weight of extracted wool. In test no. 8, the extract contained 23% of ceramides, which represented an extraction of 0.13% of ceramides over the total weight of extracted wool.
Test no. 7 has been repeated obtaining only 0.476% of total lipids over the weight of the wool, a considerably lower value to the one described in the article, and which represents an extraction of 0.18% of ceramides over the total weight of extracted wool.
Therefore, the need exists to have an extraction procedure capable of giving a better performance in obtaining the internal lipids from wool, with a high content in ceramides, and using less quantity of co-solvent as polarity-modifier of the fluid in supercritical conditions.
Thus, one object of the disclosure is a process for obtaining the internal lipids from wool fibres using wool that is substantially lanolin-free.